Add separate payer field to pay initialization fee when creating accounts

[broskicodes]

This PR is to add a payer field to all Create_ structs (CreatePost, CreateUser etc.). The payer field will allow for and account other than the authority to pay for the creation of accounts (Posts, Users etc.).

The main reason for this change is to facilitate PDAs to be the authority on user accounts.

[abishekk92]

Thanks so much for your contribution! The PR looks good, I am soft approving this for merge.

Here are couple of additions that would've been good, especially in test coverage.

1. Explicitly testing scenarios where the payer and authority are different.
2. Adding payer account in reaction/profile_metadata/user rn it is only post and connection.

Let me know, if you would like to add them, otherwise I am happy to merge this and then add the changes myself.

[broskicodes]

I'm pretty sure the PR already adds the payer account in reaction, user etc. If I missed something lmk.
I'm happy to add the changes for the tests, I start on them now.

[broskicodes]

Added the tests. Lmk when you are thinking of deploying the program with the changes and I can work on changes to the sdk packages as well :)

[abishekk92]

Thanks for making the changes, I've merged them 🎉 !

Our next deploy is going to be along side #18. It has a few breaking changes in terms of how user, profile and reaction
works.

The SDK might take a while to merge, if that's fine you can submit a PR. Otherwise, it is a small change @vjgpt or I would be happy to add them in as we make changes to the SDK for smart profile.

[abishekk92]

Update: This PR has been merged into #18 as well. Fee delegation will make a lot of things smoother re gasless etc. Thanks once again for the patch.